As the feature size of the device patterns get smaller, the critical dimension (CD) requirement of features becomes a more important criterion for stable and repeatable device performance. Allowable CD variation across a substrate has also scaled with the scaling of feature CD. With lateral dimensions scaling faster than vertical dimensions, because of issues such as device capacitance, high aspect ratios (HAR) are now prevalent in the industry. When such demanding aspect ratios and CD control are compounded with requirements of high etch selectivity, sidewall smoothness and high tool throughput, the process window for any hardware configuration can become very small. In many situations, a small process window can be found only when a number of process gases are incorporated into a complex etchant gas mixture combined with extreme hardware settings, such as very high RF bias powers, to achieve a fragile balance between sidewall passivation, etch rate and mask selectivity. However, such small process windows typically suffer from performance limitations which cannot be tuned out of the etch process with known means.
Fabrication techniques often now employ a mask stack that includes non-photo definable material layers disposed below a photo definable layer (i.e., photo resist). The non-photo definable material layers may include a carbonaceous layer, which may be of an inorganic material comprising at least 20 wt % carbon. Included in this class of materials is amorphous carbon, typically comprising greater than 50 wt % carbon, and low-k dielectrics comprising at least 20 wt % carbon content. While improved HAR etch performance is achieved with such carbonaceous masking layers, even greater etch resistance may be provided in boron-doped carbonaceous layers, which include between 1 wt. % and 40 wt. % boron (B). One example of such a boron-doped carbonaceous material is available from Applied Materials, Inc. of Santa Clara, Calif. under the trade name of advanced patterning film (APF), more specifically “APFc.”
While a boron-doped carbonaceous mask layer provides improved mask resistance to plasma processes employed to etch an underlying substrate layer (e.g., an interlayer dielectric layer (ILD), and therefore permit an aspect ratio of an opening forming in the underlying layer to be reduced through a thinning of the mask stack, this improved resistance to etching processes also renders the initial opening of the boron-doped carbonaceous layer by a plasma etch “mask open” process more difficult than for boron-free carbonaceous masking layers.
A plasma etch “mask open” process tailored to the etching of a boron-doped carbonaceous layer, such as APFc, is therefore advantageous.